The present invention relates generally to novel thermoplastic compositions. More particularly the invention relates to novel resin blends of polyphenylene ethers, polystyrene, substantially hydrogenated block copolymers of vinyl aromatic compounds and conjugated dienes, and rubbery polyacrylates.
Polyphenylene ether (oxide) resins constitute an important family of linear thermoplastic engineering resins. These resins are generally polymers of 2,6-dimethylphenol and copolymers of 2,6-dimethylphenol with 2,3,6-trimethylphenol, and may be used alone or in blends with other polymers such as styrenic resins.
Polyphenylene ethers show good compatibility with styrenic polymers over a wide range of compositions, as shown for instance by Cizek, U.S. Pat. No. 3,383,435 (5/1968). It has further been shown by Kambour in U.S. Pat. No. 3,639,508 (1/1972), Lauchlan and Shaw in U.S. Pat. No. 3,660,531 (5/1972), Carmelite and Kramer in U.S. Pat. No. 3,787,532 (1.974), Katchman and Summers in U.S. Pat. No. 3,994,856 (11/1976) and Haaf in U.S. Pat. No. 4,167,507 (1/1979) that impact strength can be improved substantially by including elastomeric block polymers of a vinyl aromatic such as styrene and a conjugated diene such as butadiene, and/or grafts of polystyrene with styrene-butadiene copolymer elastomer. Such rubber modified polystyrenes are often called HIPS (high impact polystyrene). Blends of polyphenylene ethers with HIPS, with or without inclusion of the block polymer of styrene and butadiene, are useful for many applications, such as automotive and appliance components.
However, blends of polyphenylene ethers with HIPS often have several disadvantages. Long term aging at elevated temperatures may not be sufficient for many demanding uses. Gloss and color also may not be fully satisfactory to satisfy aesthetic requirements. In general, however, applications require that improvements in heat aging, gloss and color not be made at the sacrifice of impact strength, heat distortion, tensile strength, or processing rheology.
Blends of polyphenylene ethers with polystyrene and hydrogenated block copolymers of alkenyl aromatic compounds and conjugated dienes have been described by Haaf in U. S. Pat. No. 4,423,189 (12/1983). However, the polystyrene is of a relatively low molecular weight polystyrene, which may cause a substantial lowering of both heat distortion temperature and impact strength.
High impact strength, good processability, and thermal properties may be obtained by use of specially tailored graft polymers as blending agents, as described by BASF in German Patent Applications Nos. 3434973, 3434977, 3434978, and 3434979 (1968). These German applications use special monoalkenylaromatic/diene copolymers having a polyfunctional coupling center, X, defined in further detail therein. However, such blends require the manufacture or purchase of specially tailored materials, which may add significantly to the cost of the blend and increase the difficulty of adapting the composition to specific, specialized uses.
It is an object of the invention to derive blends with an excellent balance of impact strength, heat distortion temperature, color, gloss, tensile strength, tensile modulus, melt flow, and improved thermal stability. It is also an object of the invention to accomplish the abovecited objectives by mechanical blending of readily available and relatively inexpensive multipurpose polymers.